Frequently, display devices or screens for reading measurement values of a field unit, sensor or measuring instrument have low contrast in relation to the environment. Thereby, the screens, in particular the display, become difficult to read especially under poor lighting conditions. Frequently, the displays have to be mounted at locations where little light is available, so that reading the display often proves difficult and inconvenient.
As measuring instruments are frequently used at distant locations where no power supply is available, supplying power to displays for measuring instruments is problematic.